The application of Continuous Positive Airway Pressure (CPAP) for therapy of Obstructive Sleep Apnea (OSA) was first taught by Sullivan in U.S. Pat. No. 4,944,310. In CPAP treatment of OSA, pressurized air or other breathable gas is provided to the entrance of a patients' airways at a pressure elevated above atmospheric pressure, for example in the range of 4 to 30 cm H2O to “splint” open the patients' airways and prevent obstructive apneas. Apparatus to deliver CPAP therapy typically comprise a blower, or flow generator, an air delivery conduit, hose or tube, and a patient interface, for example a mask.
In order to deliver effective therapy, a substantially leak proof seal should be maintained between the patient interface and the face of the patient. Undesirable forces applied to the mask, for example, tube drag or the weight of the mask, or components attached to the mask, tend to disrupt the seal formed between the patient interface and the patient.
Various solutions have been proposed for reducing the undesirable forces that may be applied to a mask, including tube drag. Some of these solutions include a rotating or swiveling elbow to connect the air delivery hose and the patient interface. The rotating or swiveling elbow allows some form of rotation before the tube pulls on the patient interface and disrupts the seal. Some prior art swivel and elbow arrangements use tight tolerances, which might result in friction in the movement of the swivel elbow, thus reducing the mobility and flexibility of the elbow swivel joint.
Another solution which has been proposed to reduce the application of undesirable forces on the patient interface is a headgear to provide stability to the patient interface and maintain the seal during the application of the forces, including tube drag. The headgear assembly may be designed such that the stabilizing straps are provided at an angle with respect to the patient interface and the face of the patient to counteract the undesirable forces, including tube drag. In one known mask assembly, the headgear includes a cap portion with four straps. In use, the cap portion engages the back of the patient's head and two lower straps extend between the cap portion and a nasal mask while the two upper straps extend between the cap portion and a forehead support. Such headgear assemblies may be uncomfortable for the patient and difficult to adjust to obtain a substantially leak proof seal.
Another solution for offsetting tube drag and other undesirable forces on the patient interface include clips that connect the air delivery conduit or hose to the patient's clothing, such as the patient's pajamas. Clips have also been used to connect the air delivery conduit or hose to a stationary object, such as the patient's bed, to remove or reduce tube drag affecting the mask seal.
It has also been proposed to provide a short tube between the air delivery conduit or hose to provide extra flexibility and rotation to the air delivery conduit or hose before the tube pulls on the mask.